1. Field of the Invention
The present invention relates to a portable terminal, and more particularly to an apparatus and method that can adaptively control the number of neighbor cells managed by a multi-mode portable terminal according to a system environment.
2. Description of the Related Art
In general, licensed wireless systems (or mobile communication systems such as a GSM, UMTS, and CDMA) and unlicensed wireless systems (or WLAN such as Wi-Fi, Bluetooth) have been constructed through respective networks that are in the same area. Due to relatively high speed and low service costs, unlicensed wireless systems have spread rapidly. However, unlicensed wireless systems have the disadvantages of servicing a limited area and low mobility. On the other hand, licensed wireless systems have the disadvantages of low service speed and high service costs, but the advantages of servicing a wide area and high mobility.
Recently, an unlicensed mobile access (UMA) technology, as convergence technology, has been developed to combine a licensed wireless system with an unlicensed wireless system so that they can associate with each other. Also, a multi-mode mobile station has been developed to access both a licensed wireless system and an unlicensed wireless system.
UMA technology refers to technology where a UMA network controller (UNC) provides a voice service, data service, and added services, which have been provided by the conventional mobile communication system, through an access point (AP) of an unlicensed wireless system, i.e., a wireless local area network (WLAN) AP, without changing the MSC, SGSN, GGSN, and HLR, etc. in the conventional mobile communication system.
A portable terminal supporting the UMA technology allows a user to continue to use the service, using the licensed wireless system and the unlicensed wireless system, even while entering an indoor environment where WLAN signal strength is strong. That is, the UMA technology enhances the quality of the portable terminal and allows mobile communication service providers to reduce the complexity of the system.
The portable terminal manages the cells for the licensed wireless system in such a communication environment where a mix of licensed wireless system and an unlicensed wireless system exists. The licensed wireless system is composed of a group of a certain number of neighbor cells. The portable terminal manages a part of neighbor cells whose received signal strengths are relatively strong. In this case, the portable terminal performs processes not necessary to the management of the neighbor cells and accordingly consumes electric power, although the portable terminal does not have any problem in providing communication services, such as a communication error and a service interruption, etc. Therefore, an alternative is required to efficiently manage the cells of a portable terminal in a communication environment where a mix of unlicensed wireless and licensed wireless systems exist.